1. Field of the Invention
This invention relates to the unity of a plurality of flash units for use with a camera.
2. Description of the Prior Art
When in flash photography, for the purpose of opening up dark shadows or obtaining a larger amount of flash light than that available from a single flash unit, it has been the common practice to fire two or more flash units at a time. In such a case, the use of the conventional method of combining these flash units has made it difficult to determine what aperture value is to be set in the diaphragm of the photographic lens. It has, therefore, very often happened to the beginners to make under- or over-exposure.
Also, in case when the generally known electronic flash units are used for multi-unit flash lighting, the photo detector in the camera receives the reflection of flash light from an object to be photographed and produces a de-actuating signal for every one of the flash units, thereby it being made possible to make a correct flash exposure. Since the electronic flash units generally require the photographer to adjust the size of aperture opening by his insight, if a small aperture size is set regardless of a long object distance, an under-exposure will result even though the flash units are fully fired.
To avoid this, it has been known in the art to provide for the flash unit with a metering light source for preliminary illumination. Prior to making an exposure, the object to be photographed is illuminated with preliminary flash light, and the reflected light from the object is received by a photo detector in the flash unit. The output of the photo detector is sent to the camera in which one of prescribed two or three aperture values is selected as most proper based on the ambient light intensity and the object distance sensed by the photo detector.
In application of such preliminary illumination type flash units to the multiple flash unit lighting, however, as each of the flash units in use is connected to the camera, they provide different photographic informations from each other depending on the spatial relationship between the individual flash units and the object at the same time. Therefore, which information is to be selected is necessarily a very complicated treatment.